Many different types of injection wells and recovery wells are widely used. Typical injection wells are used for water supply, groundwater control, solution mining, waste disposal, geothermal energy and to increase oil production. Typical recovery wells are used for groundwater control, capture and treatment, municipal water supplies, domestic water supplies and in the oil and geothermal industries.
Fouling at injection and recovery wells is a major problem worldwide. Chemical and biological incrustation are major causes of decreased well performance and eventual failure. Material comprising bacteria and metal oxides accumulates and clogs the wells. Iron and manganese fouling at well screens is a global problem for water supply and production wells. In addition, metals fouling is a problem at most wastewater treatment plants. For example, iron and manganese bacteria occur widely in wells open to the atmosphere when sufficient iron and/or manganese are present in the groundwater. Such bacteria plug wells by enzymatically catalyzing the oxidation of metals, using the energy to promote the growth of threadlike slimes, and accumulating large amounts of metal hydroxides, such as ferric hydroxide, in the slime. For instance, the bacteria may obtain their energy by oxidizing ferrous ions to ferric ions, which are then precipitated as hydrated ferric hydroxide on or in their mucilaginous sheaths. Iron bacteria produce accumulations of slimy material that have a gelatinous consistency. In addition, they precipitate dissolved iron and manganese. The dual effect of the growing bacteria and precipitating minerals occurs. Precipitation of the iron and rapid growth of the bacteria create a voluminous material that quickly plugs the screen pores of the sediment surrounding the well bore. The explosive growth rates of iron bacteria can render a well useless within a matter of months.
Other forms of iron bacteria induce the precipitation of iron through nonenzymatic means. These bacteria promote precipitation by mechanisms such as: raising pH; changing the redox potential of the water by algal photosynthesis; and liberating chelated iron. Some forms of iron bacteria can reduce iron to a ferrous state under anaerobic conditions.
A conventional method for reducing the amount of iron incrusting materials reaching production well screens, called the Vyredox System, uses a series of injection wells located in a circle around a production well. Oxygenated water is injected into the wells to oxidize iron in solution and promote the growth of iron bacteria so that little iron reaches the production well.
In many wells, incrusting iron cannot be removed before reaching a production well. In these cases, caustic chemicals are added to the well to clear biofouling and free the production well screen. These practices are costly, time consuming and require the production well to be brought off-line, thus disrupting service. Furthermore, the chemicals and their toxic fumes may cause serious injury to the technicians injecting them into the production well.
Other methods conventionally used to control iron bacteria are heat, explosives, ultrasonics, radiation and anoxic blocks.
Despite the above-noted efforts, need exists for the effective reduction or elimination of fouling at various types of injection and recovery wells. The present invention has been developed in view of the foregoing, and to remedy other deficiencies of the prior art.